Grid Reference Formats
OMN4 accepts and displays British National Grid references in common lettered and numeric forms. This page is the format reference; use the Search pages for the entry steps.
Format Types
| Format | Example | Use |
|---|---|---|
| Grid square letters plus digits | NY 12345 67890 | The most familiar OS map reference form. |
| Compact grid square letters plus digits | NY1234567890 | Same reference without spaces. |
| Numeric easting and northing | 312345 567890 | Useful when a dataset or specialist tool gives full numeric grid coordinates. |
In all forms, the easting comes before the northing.
Prefix-Letter References
The two-letter prefix identifies a 100 km grid square. The digits after the letters give the easting and northing within that square.
| Digits after letters | Example | Approximate precision |
|---|---|---|
| 4 digits | NY 12 67 | 1 km |
| 6 digits | NY 123 678 | 100 m |
| 8 digits | NY 1234 6789 | 10 m |
| 10 digits | NY 12345 67890 | 1 m |
Shorter references cover a larger square. Longer references identify a smaller area.
Numeric Easting And Northing
Numeric British National Grid coordinates use the full easting and northing without the two-letter square prefix.
| Value | Meaning |
|---|---|
| Easting | Distance east from the British National Grid origin, in metres. |
| Northing | Distance north from the British National Grid origin, in metres. |
For example, 312345 567890 means easting 312345, northing 567890.
When you type a full numeric easting and northing, OMN4 accepts an easting up to 700,000 m and a northing up to 1,300,000 m. Values above those limits are not accepted. These bounds apply to full numeric easting and northing entry, not to lettered grid references.
Spacing And Pasting
Spacing is for readability. OMN4 can handle common spaced and compact forms, but pasted references are easiest to interpret when the grid letters, easting, and northing are clearly separated or evenly paired.
Avoid mixing incomplete numeric coordinates with lettered references. If a value is ambiguous, check the original source and use the grid reference Search page to confirm the parsed position before relying on it.
Display Precision
The coordinate precision setting controls how much detail OMN4 shows. It does not reduce the precision of stored routes, tracks, or waypoints.